1. Field of the Invention
The present invention relates to a system for recording/reproducing data on an optical disc, and more particularly, to an apparatus and method of generating an optimum recording power for recording the data on the disc.
2. Background of the Related Art
As the storage capacity of the existing CD-ROM title is gradually reaching the uppermost limit, a digital versatile disc (DVD) is spotlighted as a new storage medium. This DVD is not so different from a compact disc (CD) in implementation principle. That is, the DVD recognizes data on the same principle as the CD that recognizes data of 0 and 1 by the difference of reflected light quantity using a laser. However, the width of data storage of the DVD is minute in comparison to the CD.
The CD or DVD is briefly classified into three types according to its function and purpose: a read only memory (ROM) type, write one read many (WORM) type on which data can be written only once, and rewritable type on which data can be repeatedly written.
Here, as the ROM type optical disc, there exist a compact disc read only memory (CD-ROM), a digital versatile disc read only memory (DVD-ROM), etc. As the WORM type optical recording medium, there exist a recordable compact disc (CD-R) on which data can be written only once, a recordable digital versatile disc (DVD-R) on which data can be written only once, etc. Also, as the rewritable optical disc, there exist a rewritable compact disc (CD-RW), a rewritable digital versatile disc (DVD-RW, DVD-RAM, and DVD+RW), etc.
The apparatus for recording/reproducing the optical disc of the CD series or of the DVD series records information on the optical disc by irradiating onto the optical disc an optical beam of a relatively large energy that can change the physical characteristic of an information recording layer, and reproduces the information from the optical disc by using the optical beam of a small energy that cannot change the physical characteristic of the information recording layer. In other words, during the recording operation, the optical disc recording/reproducing apparatus records the information by forming pits on the disc by driving a laser diode (LD) with a relatively high recording power. Here, forming of the pits on the disc as long as a predetermined length is called a write strategy.
At this time, the laser beam is incident from the opposite side of a reflecting surface where the pits are located. Accordingly, seen from the laser incident surface, the pits look like projections.
The pit has a width of 0.4˜0.6 μm, and the length of the pit and the space between the pits are determined in the range of 3T to 11T in case of the CD series and in the range of 3T to 14T in case of the DVD series. Here, T is the length of one clock pulse, 3T means three clock pulses, and 11T corresponds to the length of 11 clock pulses.
At this time, the optical disc recording/reproducing apparatus performs an optimum power calibration (OPC) process for selecting the recording power suitable for the corresponding disc in case of recording information on the rewritable optical disc such as the CD-R/RW. For this, the rewritable optical disc is provided with a power calibration area (PCA) that is a test area for determining the recording power in an unused area of the innermost periphery of the disc.
FIG. 1A is a layout diagram of a recording area of a general CD-R/CD-RW disc. The disc is divided into a clamping area 10 being clamped by a clamper, and a recording area 20 where data is recorded and reproduced. The recording area 20 includes a power calibration area (PCA) 22 for determining a proper laser power for the data to be recorded in a radius direction, a program memory area (PMA) 24 having information on the data being recorded, a lead-in area 26 for recording the information on the recorded data, a user data area 28 where user data is recorded, and a lead-out area 30 located on the outermost periphery.
The PCA 22 is divided into a test area for testing the laser power during performing the OPC, and a count area for recording the number of tests, i.e., the number of repeated recordings, as shown in FIG. 1B. Each of the test area and the count area is divided into 100 partitions so that the OPC is performed 100 times. Accordingly, the test can be performed 100 times, and if the number of tests exceeds 100, no more recording is possible even if any recording space remains.
At this time, as shown in FIG. 1C, one partition of the test area is composed of 15 sectors, and one partition, which is composed of 15 sectors, is used for one test write. That is, if the OPC is performed once, it is possible to perform the test write for 15 sectors with the laser output of 15 levels.
For this, the optical disc recording/reproducing apparatus reads an absolute time in pre-groove (ATIP) recorded on the disc, divides the recording power into 15 levels on the basis of the standard power recommended by disc makers, and writes a random or nT eight-to-fourteen modulation (EFM) signal in the test area of the PCA 22. Then, the apparatus reproduces the signal, judges the recording power to be most proper when a peak hold and a bottom hold of the reproduced signal are properly balanced, and writes data in a recordable user area 28 with this recording power value. The standard power is encoded with special information of the ATIP in the read-in area, and has a wavelength of 785 nm at a single speed.
Specifically, after recording the random data or the nT EFM signal in the test area, the apparatus checks positive and negative pits of a high-fidelity (HF) signal for each recording power as shown as a waveform in FIG. 2, and determines the power in which the value of the parameter β (β=(|A1|−|A2|)/(|A1|+|A2|)) is ‘0’, i.e., becomes symmetric, to be the optimum recording power during the reproduction.
However, since it is difficult in practice to search the recording power that is accurately ‘0’, the CD-R/RW standard recommends to determine the recording power in which the value of the parameter β is about 0.04 (i.e., 0.4%) as the optimum recording power. If a plurality of recording powers are included in the asymmetric allowable range, the apparatus determines the recording power having the minimum degree of asymmetry as the optimum recording power.
FIGS. 3A to 3C are waveform diagrams in case that the RF signal reproduced in the test area is AC-coupled.
FIG. 3A shows an asymmetric waveform appearing when the power P recorded in the test area is lower than the disc optimum power Po (i.e., P<<Po), and FIG. 3C shows an asymmetric waveform appearing when the power P recorded in the test area is higher than the disc optimum power Po (i.e., P>>Po). FIG. 3B shows a symmetric waveform appearing when the power P recorded in the test area accurately matches the disc optimum power Po (i.e., P≅Po). For example, if the data is recorded in the test area with the optimum recording power, the AC-coupled RF signal waveform becomes a symmetric waveform centering around the reference level Vref (i.e., 0) as shown in FIG. 3B.
Accordingly, if the power recorded in the test area is as shown in FIG. 3B, the value of the parameter β (β=(|A1|−|A2|)/(|A1|+|A2|)) becomes nearly ‘0’.
At this time, there may be various methods of detecting the optimum recording power. The above-described method is called an asymmetric method, and is typically applied to the CD-R disc.
Meanwhile, the CD-R is different from the CD-RW in recording material, and the asymmetric characteristic of the CD-RW is inferior to that of the CD-R. Also, in case of the CD-RW, the repeated recording characteristic should be secured, and thus it is difficult even to use a high power. Accordingly, in order to detect the optimum recording power in the CD-RW, a modulation amplitude method as shown in FIGS. 4 and 5 has been applied.
Specifically, after recording the random data or the nT EFM signal in the test area, the apparatus checks light quantities of a peak level and a bottom level of the RF signal reflected from the test area as shown as the waveform in FIG. 4. Then, the apparatus obtains the modulation amplitude (m) by computing the checked light quantities by the following equation 1. Then, the apparatus determines the optimum recording power using the modulation amplitude curve and gamma (γ) curve as shown in FIG. 5.m=(|Top|−|Bottom|)/|Top|  [Equation 1]
Here, the gamma (γ) curve is a normalized slope of the function m(Pw), and is expressed by the variation amount of the modulation amplifier and the variation amount of the recording power as in the following equation 2. The Pw is the recording power being recorded in the test area.γ=(dm/dPw)·(Pw/m)  [Equation 2]
At this time, the optimum recording power Po is determined by multiplying the recording power Pt corresponding to the predetermined gamma target (γt) value by a multiplication factor (ρ). Here, the γt value and the multiplication factor ρ, in the same manner as the above-described standard power, are predetermined during the manufacturing of the disc, and then encoded with the special information of the ATIP in the read-in area. These values may be differently determined according to the kind of disc and the maker.
Meanwhile, the DVD-series disc such as the DVD-R/RW also has the PCA area for the optimum recording as in the CD-R/RW. However, it is not prescribed in the rules how to use it, and thus it is necessary to find a method of searching the optimum recording power in the DVD-R/RW.
At this time, though the DVD-R/RW has both the land and groove signal tracks, the data is recorded only on the groove signal track. Specifically, the DVD-R/RW records position information on the groove track by pre-pitting the land track, but does not record data on the land track. At this time, the position information in the land track is called a land-pre-pit (LPP). That is, information on the physical address of the groove track is pre-recorded on the land track in the form of a pit. Also, the position information such as address information may be recorded in a wobbling shape along the boundary surface of the track.
Here, the wobbling means the recording of control information on the boundary surface of the track according to the variation of the optical beam of the corresponding laser by supplying information on the corresponding position, information on the rotating speed of the disc and so on to the power of the laser diode.
FIGS. 6A and 6B show examples of the PCA area of the DVD-R/RW. In detail, FIG. 6A shows an example of the LPP structure of the DVD-R/RW, and FIG. 6B shows an example of the LPP signal appearing in a tracking error signal detected by a push-pull method in the DVD-R/RW. In case of the DVD-R/RW, the LPP signal pre-recorded on the land is detected, and the address information representing the position of the track, sync signal, etc., are detected.
At this time, in case of the DVD-R/RW, the recording/reproduction of the data is performed in the unit of an ECC block, i.e., in the unit of 16 sectors. Also, the respective physical sector is composed of 26 sync frames. At this time, the LPP data is recorded on even sync frames (for example, 0, 2, 4, 6, . . . ) of the physical sector as shown in FIG. 7A, or on odd sync frames (for example, 1, 3, 5, 7, . . . ) of the physical sector as shown in FIG. 7B. In one physical sector is recorded the LPP data of 39 bits.
Here, for the convenience in explanation, the sector of which the LPP data is recorded on the even sync frames is called an even sector, and the sector of which the LPP data is recorded on the odd frames is called an odd sector. Also, the even sync frame is used to have the same meaning as the even position, and the odd frame is used to have the same meaning as the odd position.
As shown in FIG. 6B, the LPP data b0b1b2 carried in the start position of the even sector, i.e., in the first sync frame of the even sector, is 111, and the LPP data b0b1b2 carried in the second sync frame of the odd sector is 110. In case of the odd sector, the LPP data is recorded in the second sync frame to prevent the LPP data from overlapping with the LPP data being recorded in the start position of the even sector. Here, b0b1b2 is called sync bits for the convenience in explanation.
Accordingly, it can be discriminated using the sync bits b0,b1,b2 whether the present sector is the even sector or the odd sector. That is, if the sync bits b0,b1,b2 are 111, it is the even sector where the LPP data is recorded in the even sync frames, i.e., the even positions, of the sector. If the sync bits b0,b1,b2 are 110, it is the odd sector where the LPP data is recorded in the odd sync frames, i.e., the odd positions.
Also, the first sector of the respective ECC block is the even sector where the LPP data is always carried in the even sync frames.
Meanwhile, though the DVD-series disc such as the DVD-R/RW has the PCA area for the optimum recording as in the CD-R/RW, it is not prescribed in the rules how to use it. Accordingly, it is necessary to find a method of searching the optimum recording power in the DVD-R/RW.
Also, in case of the CD-R/RW, since the capacity of the PCA area is limited, the OPC cannot be performed even in the state that the remaining recording space exists or further recording is possible, and thus the recording cannot be performed any more. This problem may also occur in case of the DVD-R/RW.
In case of the DVD-R/RW, the physical sectors are classified into the even sectors and odd sectors as described above, and since the LPP data is carried in the second sync frame of the odd sector, the star position of the odd sector cannot be searched. Accordingly, the OPC may not be performed in the odd sectors.